<template>
	<view class="v-tabs">
		<scroll-view :id="getDomId" :scroll-x="scroll" :scroll-left="scroll ? scrollLeft : 0"
			:scroll-with-animation="scroll" :style="{ position: fixed ? 'fixed' : 'relative', zIndex }">
			<view class="v-tabs__container" :style="{
          display: scroll ? 'inline-flex' : 'flex',
          whiteSpace: scroll ? 'nowrap' : 'normal',
          background: bgColor,
          height,
          padding
        }">
				<view :class="['v-tabs__container-item', { disabled: !!v.disabled }, { active: current == i }]"
					v-for="(v, i) in tabs" :key="i" :style="{
            color: current == i ? activeColor : color,
            fontSize: current == i ? fontSize : fontSize,
            fontWeight: bold && current == i ? 'bold' : '',
            justifyContent: !scroll ? 'center' : '',
            flex: scroll ? '' : 1,
            padding: paddingItem
          }" @click="change(i)">
					<slot :row="v" :index="i">{{ field ? v[field] : v }}</slot>
				</view>
				<template v-if="!!tabs.length">
					<view 
						v-if="!pills"
						:class="['v-tabs__container-line', { animation: lineAnimation }]"
						:style="{
							background: lineColor,
							width: lineWidth + 'px',
							height: lineHeight,
							borderRadius: lineRadius,
							transform: `translate3d(${lineLeft}px, 0, 0)`
						}" />
					<view 
						v-else 
						:class="['v-tabs__container-pills', { animation: lineAnimation }]" 
						:style="{
							background: pillsColor,
							borderRadius: pillsBorderRadius,
							width: currentWidth + 'px',
							transform: `translate3d(${pillsLeft}px, 0, 0)`,
							height
						}" />
				</template>
			</view>
		</scroll-view>
		<!-- fixed 的站位高度 -->
		<view class="v-tabs__placeholder" :style="{ height: fixed ? height : '0', padding }"></view>
	</view>
</template>

<script>
	import props from './props'
	import { startMicroTask } from './utils'
	/**
	 * v-tabs
	 * @property {Number} value 选中的下标
	 * @property {Array} tabs tabs 列表
	 * @property {String} bgColor = '#fff' 背景颜色
	 * @property {String} color = '#333' 默认颜色
	 * @property {String} activeColor = '#2979ff' 选中文字颜色
	 * @property {String} fontSize = '28rpx' 默认文字大小
	 * @property {String} activeFontSize = '28rpx' 选中文字大小
	 * @property {Boolean} bold = [true | false] 选中文字是否加粗
	 * @property {Boolean} scroll = [true | false] 是否滚动
	 * @property {String} height = '60rpx' tab 的高度
	 * @property {String} lineHeight = '10rpx' 下划线的高度
	 * @property {String} lineColor = '#2979ff' 下划线的颜色
	 * @property {Number} lineScale = 0.5 下划线的宽度缩放比例
	 * @property {String} lineRadius = '10rpx' 下划线圆角
	 * @property {Boolean} pills = [true | false] 是否胶囊样式
	 * @property {String} pillsColor = '#2979ff' 胶囊背景色
	 * @property {String} pillsBorderRadius = '10rpx' 胶囊圆角大小
	 * @property {String} field 如果是对象，显示的键名
	 * @property {Boolean} fixed = [true | false] 是否固定
	 * @property {String} paddingItem = '0 22rpx' 选项的边距
	 * @property {Boolean} lineAnimation = [true | false] 下划线是否有动画
	 * @property {Number} zIndex = 1993 默认层级
	 *
	 * @event {Function(current)} change 改变标签触发
	 */
	export default {
		props,
		data() {
			return {
				lineWidth: 30,
				currentWidth: 0, // 当前选项的宽度
				lineLeft: 0, // 滑块距离左侧的位置
				pillsLeft: 0, // 胶囊距离左侧的位置
				scrollLeft: 0, // 距离左边的位置
				container: { width: 0, height: 0, left: 0, right: 0 }, // 容器的宽高，左右距离
				current: 0, // 当前选中项
				scrollWidth: 0 // 可以滚动的宽度
			}
		},
		computed: {
			getDomId() {
				const len = 16
				const $chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678' /****默认去掉了容易混淆的字符oOLl,9gq,Vv,Uu,I1****/
				const maxPos = $chars.length
				let pwd = ''
				for (let i = 0; i < len; i++) {
					pwd += $chars.charAt(Math.floor(Math.random() * maxPos))
				}
				return `xfjpeter_${pwd}`
			}
		},
		watch: {
			value: {
				immediate: true,
				handler(newVal) {
					this.current = newVal
					this.$nextTick(this.update)
				}
			},
			current(newVal) {
				this.$emit('input', newVal)
			}
		},
		methods: {
			// 切换事件
			change(index) {
				const isDisabled = !!this.tabs[index].disabled
				if (this.current !== index && !isDisabled) {
					this.current = index
					this.$emit('change', index)
				}
			},
			createQueryHandler() {
				const query = uni
					.createSelectorQuery()
					// #ifndef MP-ALIPAY
					.in(this)
				// #endif

				return query
			},
			update() {
				const _this = this
				startMicroTask(() => {
					// 没有列表的时候，不执行
					if (!this.tabs.length) return
					_this
						.createQueryHandler()
						.select(`#${this.getDomId}`)
						.boundingClientRect(data => {
							const { width, height, left, right } = data || {}
							this.container = { width, height, left, right: right - width }
							_this.calcScrollWidth()
							_this.setScrollLeft()
							_this.setLine()
						})
						.exec()
				})
			},
			// 计算可以滚动的宽度
			calcScrollWidth(callback) {
				const view = this.createQueryHandler().select(`#${this.getDomId}`)
				view.fields({ scrollOffset: true })
				view.scrollOffset(res => {
					if (typeof callback === 'function') {
						callback(res)
					} else {
						this.scrollWidth = res.scrollWidth
					}
				}).exec()
			},
			// 设置滚动条滚动的进度
			setScrollLeft() {
				this.calcScrollWidth((res) => {
					// 动态读取 scrollLeft
					let scrollLeft = res.scrollLeft
					this
						.createQueryHandler()
						.select(`#${this.getDomId} .v-tabs__container-item.active`)
						.boundingClientRect(data => {
							if (!data) return
							let curHalfWidth = (this.container.width - data.width) / 2
							let scrollDiff = this.scrollWidth - this.container.width
							scrollLeft += data.left - curHalfWidth - this.container.left
							if (scrollLeft < 0) scrollLeft = 0
							else if (scrollLeft > scrollDiff) scrollLeft = scrollDiff
							this.scrollLeft = scrollLeft
						})
						.exec()
				})
			},
			setLine() {
				this.calcScrollWidth(res => {
					const scrollLeft = res.scrollLeft
					this
						.createQueryHandler()
						.select(`#${this.getDomId} .v-tabs__container-item.active`)
						.boundingClientRect(data => {
							if (!data) return
							if (this.pills) {
								this.currentWidth = data.width
								this.pillsLeft = scrollLeft + data.left - this.container.left
							} else {
								this.lineWidth = data.width * this.lineScale
								this.lineLeft = scrollLeft + data.left + (data.width - data.width * this.lineScale) / 2 - this.container.left
							}
						})
						.exec()
				})
			}
		}
	}
</script>

<style lang="scss" scoped>
	.v-tabs {
		width: 100%;
		box-sizing: border-box;
		overflow: hidden;

		::-webkit-scrollbar {
			display: none;
		}

		&__container {
			min-width: 100%;
			position: relative;
			display: inline-flex;
			align-items: center;
			white-space: nowrap;
			overflow: hidden;

			&-item {
				flex-shrink: 0;
				display: flex;
				align-items: center;
				height: 100%;
				position: relative;
				z-index: 10;
				transition: all 0.3s;
				white-space: nowrap;

				&.disabled {
					opacity: 0.5;
					color: #999;
				}
			}

			&-line {
				position: absolute;
				left: 0;
				bottom: 0;
			}

			&-pills {
				position: absolute;
				z-index: 9;
			}

			&-line,
			&-pills {
				&.animation {
					transition: all 0.3s linear;
				}
			}
		}
	}
</style>